The task of an oil supply device of an automatic planetary transmission is to provide a sufficiently high oil volume flow and a sufficiently high operating pressure for actuating the friction shift elements, i.e. the shift clutches and shift brakes, as well as for lubricating and cooling the moving parts of the automatic transmission during the operation of the motor vehicle of interest. For this purpose, an oil supply device usually has at least one oil pump, by means of which hydraulic oil can be delivered from a reservoir (oil pan) to a main pressure line and to a secondary pressure line. The shift control valves, which are primarily integrated into a valve block, are connected to the main pressure line that is under a relatively high working pressure (main pressure PHD) that can be variably adjusted via a main pressure valve, wherein the shift cylinders of the friction shift elements are pressurized via the shift control valves from the main pressure line in order to engage gears and are discharged into a secondary pressure line or a depressurized line connected to the oil pan via these valves in order to disengage gears. The cooling and lubricating points of the automatic transmission are connected to the secondary pressure line that is under relatively low pressure (secondary pressure pSD).
The oil pump is usually configured as a so-called fixed displacement pump, which delivers a constant oil volume per revolution of an associated drive element. Known designs of oil pumps of this type include the gear pump, the rotor pump (sickle pump) and the vane pump. The oil pump may be driven mechanically by a drive connection to a driven shaft, such as the drive shaft of the driving motor or the input shaft of the automatic transmission, or electrically by a drive connection to an associated electric motor. The delivery volume flow and the producible working pressure of the oil pump increase with the rotational speed of the driving component (driven shaft or electric motor) and, in the case of the mechanical drive, are determined by the rotational speed of the respective shaft. In contrast, in the case of the electric drive, the delivery volume flow and the producible working pressure are variably controllable within the control range of the associated electric motor. The delivery power drawn from the driving component for driving the oil pump increases with the delivery volume flow and the working pressure at the output side, against which the oil volume flow is pumped into a pressure line.
As a result of the designs perfected in decades of use, the known types of fixed displacement pumps have high functional reliability and long durability. The disadvantage with fixed displacement pumps of this type is, however, that they cannot generate an appreciable oil volume flow and no high working pressure below a minimum input speed, which may result in an undersupply of the automatic transmission with hydraulic oil, in particular when the driving motor is shut off and when the vehicle is stationary. A further disadvantage of known fixed displacement pumps is that, as they have been configured for providing a high delivery rate even at lower input speeds, they deliver an excessively high oil volume flow at higher input speeds, most of which then must be discharged largely unused, resulting in poor transmission efficiency. Different solutions to improve the oil supply of automatic transmissions have therefore been proposed.
A first known solution consists of designing a mechanically driven adjustable oil pump so that the delivery rate thereof may be varied or maintained constant independently of the input speed within an adjustment range that is specified by the design. Such an oil supply device of an automatic planetary transmission having a mechanically driven, adjustable high pressure oil pump has, for example, been described in DE 600 08 588 T2. In this oil supply device, it is provided that the delivery rate of the high pressure oil pump, and thus the working pressure in the connected main pressure line, is regulated by means of a pressure controlled regulating valve, which is actuated by the working pressure of the main pressure line and by the working pressure of a secondary pressure line. For this purpose, it is provided that the working pressure of the main pressure line is conducted into an associated output actuating cylinder via the regulating valve for the inverse control of the delivery rate of the high pressure oil pump. Although an unnecessarily high delivery rate and the resultant reduction of the transmission efficiency is avoided at higher input speeds by the adjustability of the oil pump, the complexity of a device of this type of oil pump and the associated control device is, however, relatively high and may be associated with a high susceptibility to malfunction.
A further known solution of avoiding delivery rate problems consists of arranging and equipping a single oil pump, such that it may be driven mechanically via a drive shaft of the powertrain or via an associated electric motor, as and when needed.
A hybrid drive of a motor vehicle having an oil supply device of this type is known, for example, from DE 199 17 665 A1. In it, an oil pump is provided that is arranged on the drive shaft of an internal combustion engine and may be driven by the drive shaft of the internal combustion engine via the engagement of an associated clutch and by an associated electric motor when the clutch is disengaged. The oil pump may be configured to provide a relatively low delivery rate and, in case of a higher oil requirement, in particular when the internal combustion engine is shut off or running at low rotational speed, may be driven by the electric motor at a higher rotational speed with an open clutch.
A further hybrid drive of a motor vehicle having an oil supply device of this type has been described in DE 101 60 466 C1. In it, an oil pump is provided that is arranged at the input shaft of an automatic transmission and may be mechanically driven by the input shaft of the automatic transmission via a first overrunning clutch and by the rotor of an associated electric motor via a second overrunning clutch. The oil pump is respectively driven via the faster of the two driving elements, so that a sufficiently high delivery rate of the oil pump may be achieved by a corresponding drive via the electric motor, even with a stationary vehicle or at a low driving speed. The disadvantage of an oil pump of this type is the technical complexity and the required space, as well as the susceptibility to malfunction of both alternative drive branches.
Oil supply devices have therefore also been proposed that comprise a main oil pump mechanically drivably connected to a drive shaft of the powertrain, and an auxiliary oil pump that may be driven by a controllable electric motor. A corresponding oil supply device of the automatic transmission of a hybrid powertrain has been described in U.S. Pat. No. 6,692,402 B2. In the associated method for controlling the auxiliary pump, it is provided that the working pressure in a main pressure line is monitored and that the auxiliary oil pump is activated when the working pressure drops below a first limit value due to an insufficient delivery capacity of the main oil pump that is drivably connected to the input shaft of the automatic transmission, in particular due to increased consumption as a result of shifting effects. The auxiliary oil pump is deactivated again when the working pressure increases above a second limit value, in particular after completing a gear change. In order to avoid an excessively high delivery rate of the auxiliary oil pump, and consequently, too high a working pressure, the oil temperature of the hydraulic oil to be delivered is determined, and the driving power of the electric motor is set as a function of the oil temperature, which is to say increased with increasing oil temperature and reduced with decreasing oil temperature.
A further oil supply device having a mechanically drivable main oil pump and an electrically drivable auxiliary oil pump has been known from DE 10 2005 013 137 A1. It is provided therein that the main oil pump, which is drivably connected to the drive shaft of the internal combustion engine, is supported by the auxiliary oil pump such that it at least delivers a sufficient oil volume flow for cooling the start-up element during start-up. The disadvantage of these known oil supply devices and/or control methods is that the main oil pump is only supported and/or supplemented by the operation of the auxiliary oil pump in certain operating states. The basic problems of an insufficient delivery rate of the main oil pump at low input speeds and excessively high delivery rate at high input speeds have, however, not been comprehensively solved in this way.